In recent years, the value of information has been improving in line with development of the diffusion of IT (Information Technology) to corporations. The corporate management cannot be realized without the information such as customer information, business information and management information or the like. Therefore, it can be said that the information is now assets of the corporation.
In a storage apparatus which stores the above-mentioned information, protective measures such as backup of information or the like are applied. And, in order to secure the business continuity coping with disasters and acts of terrorism, the storage apparatuses are installed in remote locations in a dispersive way.
A memory storage which has high disaster tolerance, and is capable of data backup with “guaranteeing the orderliness” is disclosed by Japanese Patent Application Laid-Open No. 2012-003600 (it is hereinafter referred to as “patent document 1”). Here, “guaranteeing the orderliness” means that, when performing backup of a plurality of data, the order of the data is maintained, that is, information about the data order is maintained. For example, the orderliness of data is guaranteed when the data is stored so that the data is written in following the data order, and when reading the data, the data to be read is read in the order following the original data order. The memory storage described in patent document 1 stores the data which is stored in the first storage means also in the second storage means. The memory storage of patent document 1 includes a means configured to migrate the data which is stored in the second storage means to the third storage means, and a means configured to restore the data which has been migrated to the third storage means to the second storage means according to the status of use of the second storage means. Further, the memory storage of patent document 1 includes a means configured to output and store the data which is stored in the second storage means in a copy destination apparatus which is communicably connected to own apparatus.
That is, the memory storage of patent document 1 uses the first storage means as a main memory and uses the second storage means as a temporary memory when copying the data to the copy destination apparatus. The memory storage of patent document 1, according to the status of use of the second storage means, temporarily migrates the data stored in the second storage means to the third storage means, and restores the data having been migrated to the third storage means to an unused area of the second storage means.
The memory storage of patent document 1 avoids the excess in the storage capacity of the second storage means (a temporary memory), which is used when copying the data to the copy destination apparatus, by the third storage means (temporary migration).
A storage subsystem including a first storage subsystem which is connected with a plurality of host apparatuses, and a second storage subsystem which is connected with the first storage subsystem is disclosed by Japanese Patent Application Laid-Open No. 2002-334049 (it is hereinafter referred to as “patent document 2”). The storage subsystem of patent document 2 holds write data doubly in the first and second storage subsystems by copying the write data to the first storage subsystem from a host apparatus to the second storage subsystem.
In the first storage subsystem, a data buffer is provided for each of the host apparatuses and an “occupancy ratio” is calculated for each data buffer. Here, the “occupancy ratio” means the percentage of an amount of the write data which has not been copied to the second storage subsystem in the storage capacity of the data buffer. A threshold value for judging the amount of the write data which has not been copied is set for each data buffer.
When the occupancy ratio of any of the data buffers of the first storage subsystem has exceeded the threshold value, the first storage subsystem restricts inflow of the write data from the host apparatus corresponding to the data buffer in which the occupancy ratio has exceeded the threshold value.
Specifically, the first storage subsystem delays a response of writing completion to the write data from the host apparatus corresponding to the data buffer in which the occupation ratio has exceeded the threshold value.
That is, technology of patent document 2 restricts the inflow volume of the write data by delaying the response of writing completion and suppressing writing of the next data. In the technology of patent document 2, while restricting inflow of the write data, the data from the first storage subsystem is copied to the second storage subsystem. The technology of patent document 2 decreases the data volume of non-copied data in the data buffer, and restores from the state in which the occupancy ratio of the data buffer has exceeded the threshold value to the state in which the occupancy ratio does not exceed.